Option Explicit

' Operating System version information declares

Private Const VER_PLATFORM_WIN32_NT = 2
Private Const VER_PLATFORM_WIN32_WINDOWS = 1

Private Type OSVERSIONINFO
dwOSVersionInfoSize As Long
dwMajorVersion As Long
dwMinorVersion As Long
dwBuildNumber As Long
dwPlatformId As Long
szCSDVersion As String * 128 ' Maintenance string
End Type

Private Declare Function GetVersionEx Lib "kernel32" _
Alias "GetVersionExA" (lpVersionInformation As OSVERSIONINFO) As Long

' Time Zone information declares

Private Type SYSTEMTIME
wYear As Integer
wMonth As Integer
wDayOfWeek As Integer
wDay As Integer
wHour As Integer
wMinute As Integer
wSecond As Integer
wMilliseconds As Integer
End Type

Private Type REGTIMEZONEINFORMATION
Bias As Long
StandardBias As Long
DaylightBias As Long
StandardDate As SYSTEMTIME
DaylightDate As SYSTEMTIME
End Type

Private Type TIME_ZONE_INFORMATION
Bias As Long
StandardName(0 To 63) As Byte ' used to accommodate Unicode strings
StandardDate As SYSTEMTIME
StandardBias As Long
DaylightName(0 To 63) As Byte ' used to accommodate Unicode strings
DaylightDate As SYSTEMTIME
DaylightBias As Long
End Type

Private Const TIME_ZONE_ID_INVALID = &HFFFFFFFF
Private Const TIME_ZONE_ID_UNKNOWN = 0
Private Const TIME_ZONE_ID_STANDARD = 1
Private Const TIME_ZONE_ID_DAYLIGHT = 2

Private Declare Function GetTimeZoneInformation Lib "kernel32" _
(lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long

Private Declare Function SetTimeZoneInformation Lib "kernel32" _
(lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long

' Registry information declares
Private Const REG_SZ As Long = 1
Private Const REG_BINARY = 3
Private Const REG_DWORD As Long = 4

Private Const HKEY_CLASSES_ROOT = &H80000000
Private Const HKEY_CURRENT_USER = &H80000001
Private Const HKEY_LOCAL_MACHINE = &H80000002
Private Const HKEY_USERS = &H80000003

Private Const ERROR_SUCCESS = 0
Private Const ERROR_BADDB = 1
Private Const ERROR_BADKEY = 2
Private Const ERROR_CANTOPEN = 3
Private Const ERROR_CANTREAD = 4
Private Const ERROR_CANTWRITE = 5
Private Const ERROR_OUTOFMEMORY = 6
Private Const ERROR_ARENA_TRASHED = 7
Private Const ERROR_ACCESS_DENIED = 8
Private Const ERROR_INVALID_PARAMETERS = 87
Private Const ERROR_NO_MORE_ITEMS = 259

Private Const KEY_ALL_ACCESS = &H3F

Private Const REG_OPTION_NON_VOLATILE = 0

Private Declare Function RegOpenKeyEx Lib "advapi32.dll" _
Alias "RegOpenKeyExA" ( _
ByVal hKey As Long, _
ByVal lpSubKey As String, _
ByVal ulOptions As Long, _
ByVal samDesired As Long, _
phkResult As Long) _
As Long

Private Declare Function RegQueryValueEx Lib "advapi32.dll" _
Alias "RegQueryValueExA" ( _
ByVal hKey As Long, _
ByVal lpszValueName As String, _
ByVal lpdwReserved As Long, _
lpdwType As Long, _
lpData As Any, _
lpcbData As Long) _
As Long

Private Declare Function RegQueryValueExString Lib "advapi32.dll" _
Alias "RegQueryValueExA" ( _
ByVal hKey As Long, _
ByVal lpValueName As String, _
ByVal lpReserved As Long, _
lpType As Long, _
ByVal lpData As String, _
lpcbData As Long) _
As Long

Private Declare Function RegEnumKey Lib "advapi32.dll" _
Alias "RegEnumKeyA" ( _
ByVal hKey As Long, _
ByVal dwIndex As Long, _
ByVal lpName As String, _
ByVal cbName As Long) _
As Long

Private Declare Function RegCloseKey Lib "advapi32.dll" ( _
ByVal hKey As Long) _
As Long

' Registry Constants
Const SKEY_NT = "SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones"
Const SKEY_9X = "SOFTWARE\Microsoft\Windows\CurrentVersion\Time Zones"

' The following declaration is different from the one in the API viewer.
' To disable implicit ANSI<->Unicode conversion, it changes the
' variable types of lpMultiByteStr and lpWideCharStr to Any.
'
Private Declare Function MultiByteToWideChar Lib "kernel32" ( _
ByVal CodePage As Long, _
ByVal dwFlags As Long, _
lpMultiByteStr As Any, _
ByVal cchMultiByte As Long, _
lpWideCharStr As Any, _
ByVal cchWideChar As Long) As Long

' The above Declare and the following Constants are used to make
' this sample compatible with Double Byte Character Systems (DBCS).
Private Const CP_ACP = 0
Private Const MB_PRECOMPOSED = &H1
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" ( _
ByRef Destination As Any, _
ByRef Source As Any, _
ByVal numbytes As Long)
Dim SubKey As String

Private Sub Form_Load()
Dim lRetVal As Long, lResult As Long, lCurIdx As Long
Dim lDataLen As Long, lValueLen As Long, hKeyResult As Long
Dim strvalue As String
Dim osV As OSVERSIONINFO

' Win9x and WinNT have a slightly different registry structure. Determine
' the operating system and set a module variable to the correct subkey.

osV.dwOSVersionInfoSize = Len(osV)
Call GetVersionEx(osV)
If osV.dwPlatformId = VER_PLATFORM_WIN32_NT Then
SubKey = SKEY_NT
Else
SubKey = SKEY_9X
End If

lRetVal = RegOpenKeyEx(HKEY_LOCAL_MACHINE, SubKey, 0, _
                  KEY_ALL_ACCESS, hKeyResult)

If lRetVal = ERROR_SUCCESS Then

lCurIdx = 0
lDataLen = 32
lValueLen = 32

Do
 strvalue = String(lValueLen, 0)
 lResult = RegEnumKey(hKeyResult, lCurIdx, strvalue, lDataLen)

 If lResult = ERROR_SUCCESS Then
    List1.AddItem Left(strvalue, lValueLen)
 End If

 lCurIdx = lCurIdx + 1

Loop While lResult = ERROR_SUCCESS

RegCloseKey hKeyResult
Else
List1.AddItem "Could not open registry key"
End If
End Sub

Private Sub List1_DblClick()
Dim TZ As TIME_ZONE_INFORMATION, oldTZ As TIME_ZONE_INFORMATION
Dim rTZI As REGTIMEZONEINFORMATION
Dim bytDLTName(32) As Byte, bytSTDName(32) As Byte
Dim cbStr As Long, dwType As Long
Dim lRetVal As Long, hKeyResult As Long, lngData As Long

lRetVal = RegOpenKeyEx(HKEY_LOCAL_MACHINE, SubKey & "\" & List1.Text, _
                   0, KEY_ALL_ACCESS, hKeyResult)

If lRetVal = ERROR_SUCCESS Then
lRetVal = RegQueryValueEx(hKeyResult, "TZI", 0&, ByVal 0&, _
                          rTZI, Len(rTZI))

If lRetVal = ERROR_SUCCESS Then
 TZ.Bias = rTZI.Bias
 TZ.StandardBias = rTZI.StandardBias
 TZ.DaylightBias = rTZI.DaylightBias
 TZ.StandardDate = rTZI.StandardDate
 TZ.DaylightDate = rTZI.DaylightDate

 cbStr = 32
 dwType = REG_SZ

 lRetVal = RegQueryValueEx(hKeyResult, "Std", _
             0&, dwType, bytSTDName(0), cbStr)

 If lRetVal = ERROR_SUCCESS Then
    Call MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, _
       bytSTDName(0), cbStr, TZ.StandardName(0), 32)
 Else
    RegCloseKey hKeyResult
    Exit Sub
 End If

 cbStr = 32
 dwType = REG_SZ

 lRetVal = RegQueryValueEx(hKeyResult, "Dlt", _
             0&, dwType, bytDLTName(0), cbStr)

 If lRetVal = ERROR_SUCCESS Then
    Call MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, _
       bytDLTName(0), cbStr, TZ.DaylightName(0), 32)
 Else
    RegCloseKey hKeyResult
    Exit Sub
 End If

 lRetVal = GetTimeZoneInformation(oldTZ)

 If lRetVal = TIME_ZONE_ID_INVALID Then
    MsgBox "Error getting original TimeZone Info"
    RegCloseKey hKeyResult
    Exit Sub
 Else
 If TZ.DaylightDate.wMonth <> 0 And TZ.DaylightBias <> 0 Then
    lRetVal = SetTimeZoneInformation(TZ)
 Else
   Call CopyMemory(TZ.DaylightName(0), TZ.StandardName(0), 64)
   TZ.DaylightBias = 0
   lRetVal = SetTimeZoneInformation(TZ)
 End If
    MsgBox "Time Zone Changed, Click OK to restore"
    lRetVal = SetTimeZoneInformation(oldTZ)
 End If
End If

RegCloseKey hKeyResult
End If
End Sub